1. Field of the Invention
The present invention relates generally to cab-over vehicles and more specifically to a internal combustion engine cooling system for use in cab-over type vehicles.
2. Description of the Prior Art
As shown in FIG. 1 of the drawings, in cab-over type vehicles, due to the location of the engine beneath the driver's seat and front passenger's seat, the requirement for leg room immediately forward of the seats causes the engine to be enclosed as shown. This induces a problem that natural ventilation of the engine compartment is greatly inhibited as the air, after flowing under the forward passenger floor, must then change direction (as shown by the arrows). Subsequently, after passing over the radiator and engine, the air is again required to change direction and flow downwardly so as to pass under the vehicle. Further, in compact cab-over vehicles the amount of leg room tends to be insufficient due to the location of the radiator forward of the engine. Accordingly, to increase the amount of space available in the front of such vehicles relocation of the engine radiator to another site would prove extremely beneficial. However, with convential type cooling systems location of the radiator distal from the engine induces the problem that the relatively long conduits between the engine and the radiator increase the load on the engine water pump. Further, if the radiator is disposed on top of the vehicle not only does the increased flow restriction caused by the long conduiting between the engine and radiator increase the load on the pump, but the water must be lifted vertically through a notable distance from the engine to the roof. Moreover, the bulk of conventional water circulation type cooling system radiators causes aesthetic disposition of same in such locations extremely difficult.
FIG. 2 of the drawings shows an arrangement disclosed in U.S. Pat. No. 1,806,382 issued on May 19, 1931 in the name of L.P. Barlow wherein it has been proposed to cool the engine via permitting the engine coolant to boil and condensing the vapor produced in a radiator disposed on the roof of the vehicle. This concept while being highly compatible with the design needs of the cab-over type vehicles has suffered from the drawback that the radiator heat exchange efficiency is rapidly lost due to the inclusion of air in the system. This air which leaks in during non-use tends to form embolism-like bubbles which hinder the flow of steam or like vapor and which reduce the surface area available for heat exchange. In an attempt to overcome this problem a steam trap is provided to permit air to be vented and coolant loss minimized. However, due to the tendancy for air to rise when heated, once the system becomes contaminated with air, purging of same from the relatively high positioned radiator using coolant vapor has not been possible to any acceptable extent.
Further, when this system is operated at high altitudes, the rate at which coolant is lost from the system through the steam trap is unacceptably high.
Various other so called "vapor cooled" engine systems have been developed (set forth hereinblow) but none have proven successful due to air contamination, loss of coolant and/or undue complexity.
FIG. 3 shows an arrangement disclosed in Japanese Patent Application Second Provisional Publication No. Sho 57-57608. This arrangement has attempted to vaporize a liquid coolant and use the gaseous form thereof as a vehicle for removing heat from the engine. In this system the radiator 1 and the coolant jacket 2 are in constant and free communication via conduits 3 and 4 whereby the coolant which condenses in the radiator 1 is returned to the coolant jacket 2 little by little under the influence of gravity.
This arrangement has suffered from the drawbacks that the radiator, depending on its position with respect to the engine proper tends to be at least partially filled with liquid coolant. This greatly reduces the surface area via which the gaseous coolant (for example steam) can effectively release its latent heat of vaporization and accordingly condense and thus has lacked any notable improvement in cooling efficiency.
Further, with this system in order to maintain the pressure within the coolant jacket and radiator at atmospheric level, a gas permeable water shedding filter 5 is arranged as shown, to permit the entry of air into and out of the system. However, this filter permits gaseous coolant to gradually escape from the system, inducing the need for frequent topping up of the coolant level.
A further problem with this arrangement has come in that some of the air, which is sucked into the cooling system as the engine cools, tends to dissolve in the water, whereby upon start up of the engine, the dissolved air tends to form small bubbles in the radiator which adhere to the walls thereof forming an insulating layer. The undissolved air tends to collect in the upper section of the radiator and inhibit the convention-like circulation of the vapor from the cylinder block to the radiator. This of course further deteriorates the performance of the device.
European Patent Application Provisional Publication No. 0 059 423 published on Sept. 8, 1982 discloses another arrangement wherein, liquid coolant in the coolant jacket of the engine, is not circulated therein and permitted to absorb heat to the point of boiling. The gaseous coolant thus generated is adiabatically compressed in a compressor so as to raise the temperature and pressure thereof and is introduced into a heat exchanger. After condensing, the coolant is temporarily stored in a reservoir and recycled back into the coolant jacket via a flow control valve.
This arrangement has suffered from the drawback in that air tends to leak into the system upon cooling thereof. This air tends to be forced by the compressor along with the gaseous coolant into the radiator. Due to the difference in specific gravity, the air tends to rise in the hot environment while the coolant which has condensed moves downwardly. The air, due to this inherent tendency to rise, forms large bubbles of air which cause "embolism-like" blockages in the radiator and badly impair the heat exchange ability thereof.
U.S. Pat. No. 4,367,699 issued on Jan. 11, 1983 in the name of Evans (see FIG. 4 of the drawings) discloses an engine system wherein the coolant is boiled and the vapor used to remove heat from the engine. This arrangement features a separation tank 6 wherein gaseous and liquid coolant are initially separated. The liquid coolant is fed back to the cylinder block 7 under the influence of gravity while the "dry" gaseous coolant (steam for example) is condensed in a fan cooled radiator 8. The temperature of the radiator is controlled by selective energizations of the fan 9 to maintain a rate of condensation therein sufficient to maintain a liquid seal at the bottom of the device. Condensate discharged from the radiator via the above mentioned liquid seal is collected in a small reservoir-like arrangement 10 and pumped back up to the separation tank via a small pump 11.
This arrangement, while providing an arrangement via which air can be initially purged to some degree from the system tends to, due to the nature of the arrangement which permits said initial non-condensible matter to be forced out of the system, suffer from rapid loss of coolant when operated at relatively high altitudes. Further, once the engine cools, air is relatively freely admitted back into the system. The provision of the separation tank 6 also renders engine layout difficult. In the event that the radiator of this system is placed on the vehicle roof, the difficulty of purging the air therefrom increases.
Japanese Patent Application First Provisional Publication No. Sho. 56-32026 (see FIG. 5 of the drawings) discloses an arrangement wherein the structure defining the cylinder head and cylinder liners are covered in a porous layer of ceramic material 12 and coolant sprayed into the cylinder block from shower-like arrangements 13 located above the cylinder heads 14. The interior of the coolant jacket defined within the engine proper is essentially filled with gaseous coolant during engine operation during which liquid coolant sprayed onto the ceramic layers 12. However, this arrangement has proved totally unsatisfactory in that upon boiling of the liquid coolant absorbed into the ceramic layers the vapor thus produced escaping into the coolant jacket inhibits the penetration of liquid coolant into the layers whereby rapid overheat and thermal damage of the ceramic layers 12 and/or engine soon results. Further, this arrangement is plagued with air contamination and blockages in the radiator similar to the compressor equipped arrangement discussed above.
In summary although the basic concepts of open and closed "vapor cooling" systems wherein the coolant is boiled to make use of the latent heat of evaporation thereof and condensed in a suitable heat exchanger, is known, the lack of a control system which is both sufficiently simple as to allow practical use and which overcomes the various problems plaguing the prior art is wanting. Placing the radiator well above the engine (such as on the vehicle roof) has increased the difficulty of removing contaminating air therefrom.